(1) Field of the Invention
The present invention relates to a polycarbodiimide copolymer and a process for production thereof. More particularly, the present invention relates to a polycarbodiimide copolymer wherein a liquid rubber structure is introduced in the main chain of a polycarbodiimide resin and which is improved, as compared with polycarbodiimide resins, in thermoformability when made into a solid such as a powder or granules while having the excellent heat resistance inherently possessed by polycarbodiimide resins, as well as to a process for producing the polycarbodiimide copolymer.
(2) Description of the Prior Art
Polycarbodiimide resins, particularly aromatic polycarbodiimide resins are known as a highly heat-resistant resin. Their varnishes, powders, etc. are in use as a molding material, a stabilizer to hydrolysis, etc. The powders and granules of polycarbodiimide resins, however, are known to be inferior in thermal flowability when used as a molding material.
With respect to the powders of polycarbodiimide resin, there is disclosed in, for example, J. Appl. Poly. Sci., 21, 1999 (1977) and JP-B-52-16759, a process for isolating a polycarbodiimide resin in a powdery state by reacting 4,4'-diphenylmethane diisocyanate with an organic monoisocyanate (a molecular weight regulator) in the presence of a carbodiimidization catalyst in an inert organic solvent.
That is, in the above J. Appl. Poly. Sci., it is described that the above reaction is conducted in a xylene solvent, then the reaction system is cooled to room temperature, the resulting solid precipitate is isolated by filtration, the filtrate is poured into an excess hexane, the resulting solid precipitate is isolated by filtration, and the two precipitates are combined and dried to obtain a powder (this powder is called "terminal-blocked polycarbodiimide"). In the above literature are also described the improved flowability under heating and pressure and other properties of the powder.
The powder of terminal-blocked polycarbodiimide resin contains low-molecular compounds such as monocarbodiimide [formed by reaction of two monoisocyanate molecules (monoisocyanate is a terminal blocking agent)], low-molecular carbodiimide and the like; therefore, when the powder is molded or used at high temperatures, the low-molecular compounds contained therein are vaporized to cause foaming and blistering or emit an offensive odor.